Adapter is the term I was trying to think of, though according to that Wikipedia article it's synonymous with wrapper.

Thanks — I can now write my doc block

PCSpectra
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2011-07-08T13:06:25Z —
#5

Adapter and wrapper are essentially two of the same, but adapter is the formal term usually used in patterns books.

Also of possible interest is the strangler application, which Fowler describes as a process of gradually "strangling" legacy code and replacing with new code (As opposed to rewriting an entire system before going live):